This invention relates to a guide bar for a saw chain on a chain saw and more specifically to a guide bar having a replaceable nose section.
A guide bar for a chain saw supports a saw chain that travels at high speeds while subjected to cutting loads. A considerable force is required to pull the chain around the bar and causes severe wear at the nose of the bar. Also, it is common that bars may be damaged at the nose portion. Accordingly, this wearing and/or damage at the nose of the bar often determines the reasonable life of the typical guide bar.
The bar is a fairly expensive item to the chain saw user. Thus, there have been a number of attempts to design guide bars having replaceable nose sections which can multiply the usable life of the main portion of the bar and substantially reduce the user's costs.
A number of disadvantages have been experienced in prior bars with replaceable nose sections. To obtain sufficient rigidity in the interconnection between the main body section and the nose section of such a bar, it is desirable to provide a portion of one section of the bar which slips into or onto a portion of the other section. This has generally required either that both sections be machined to provide such interfitting relationship or that one portion be provided with additional spacer elements between parts to provide a spacing therebetween.
A general object of the present invention is to provide a novel guide bar in which a sliding interconnection, or fit, can be provided with a minimum of machining or spacing elements required. More specifically, the invention provides a bar with a nose section which consists of a pair of opposed, facing plates, at least one of the plates having a central portion deformed laterally toward the other of the plates from the plane of the remainder portions thereof. The two plates are secured together in the region of deformation whereby peripheral edge margins of the plates are spaced apart to define a chain-receiving groove therein. The nose section has rearwardly extending tongue portions also with peripheral edge margins spaced apart by the deformation of central portions of the plates, which spaced portions of the tongues may slide onto a flange formed in the main body section of the bar to provide alignment and a rigid interconnection therebetween.
A further object of the present invention is to provide such a novel bar in which recesses are provided in opposed faces of the main body section of the bar. These recesses have edge margins which diverge on progressing forwardly in the bar and the tongue portions of the nose section have complementary diverging edge margins which cooperate with the diverging edge margins of the recesses to provide desired alignment between the sections.
A still further object of the present invention is to provide such a novel guide bar in which generally aligned apertures are defined in the tongue portions of the plates of the nose section and a portion of the main body section of the bar for receiving a securing member therebetween. The securing member may be a combination hub unit of a shape to fit in the apertures and having a bore therethrough, with an expander member sized for driving into the bore in the hub member for expanding the same into the apertures and holding it securely therein. The apertures in the nose section may be slightly offset longitudinally of the bar from the aperture in the body section. On expansion of the hub the sections are drawn tightly together.